The present invention relates to a valve for controlling gas flow to ventilator or physiotherapy apparatus.
Examples of known valves for use in ventilation apparatus are discussed hereinbelow.
EP-A-0373153 discloses a ventilator apparatus for use in the ventilation of the lungs of a patient, which apparatus comprises a ventilator enclosure for receiving the chest region of a patient""s body connected via a fluid control valve both to a positive fluid pressure source and a negative fluid pressure source. The valve comprises a main port connected to the ventilator enclosure, subsidiary ports connected to a respective one of the positive and negative pressure sources, and a shutter mechanism which alternately permits the application of positive and negative pressure to the ventilator enclosure. With this arrangement, the use of separate positive and negative pressure sources, such as a pair of gas blowers, is required. Ideally, however, for efficiency the use of a single gas blower is desired. The arrangement disclosed in EP-A-0373153 does not allow for the use of a single gas blower having its positive pressure side connected to one subsidiary port of the valve and its negative pressure side connected to the other subsidiary port of the valve since a closed loop would be created with no vent to the exterior of the valve.
WO-94/27553 discloses a fluid control valve which allows the positive and negative pressure sides of a single fluid supply to be connected to a closed system, such as a ventilator enclosure, so as to permit the generation alternately of a positive and negative pressure in the closed system. The valve comprises a valve body having first and second subsidiary ports for connection to the ventilator enclosure, and a valve means which comprises a shutter mechanism for selectively connecting either the first subsidiary port to the main port whilst blocking the connection path between the second subsidiary port and the main port, or connecting the second subsidiary port to the main port whilst blocking the connection path between the first subsidiary port and the main port. In order to permit connection to a closed system, the valve means includes a further shutter mechanism which is coupled for synchronous movement with the first-mentioned shutter mechanism so as to provide a temporary connection to the exterior of the valve from whichever of the first and second subsidiary ports is blocked off from the main port. Such an arrangement allows the use of a single fluid supply, and by the use of a shutter mechanism, which is capable of progressively closing the path between the main port and the respective subsidiary port, greater control over the shape and intensity of the positive and negative pressure pulses applied to the main port is provided. However, the arrangement cannot provide a supply of positive and negative fluid pressure at frequencies exceeding 5-6 Hz. The reason for this is that to generate alternately a positive and negative pressure at the main port requires the repeated reversal of the direction of rotation of the shutter mechanism and the frequency of operation of that valve is limited to the rate at which the direction of rotation of the control motor, and hence shutter mechanism, can be reversed. Reversal of the direction of rotation of the motor requires the motor to be brought to a stop, and this introduces an unavoidable minimum time delay. Continuous rotation of the shutter mechanism employed in the valve disclosed in WO-94/27553 is not possible since, over a sector of the rotation of the shutter mechanism, both of the subsidiary ports which are connected to the blower inlet and the blower outlet would at the same time be connected to the main port.
UK patent application No. 9522222.0 discloses a fluid control valve comprising a body having first and second ports for connection to a positive fluid pressure source and a negative fluid pressure source and an outlet port for connection to a device such as a ventilator apparatus, and a cylindrical valve member rotatable with respect to the body which is adapted selectively to interconnect the first and second ports to the outlet port. Instead of requiring a shutter mechanism which is oscillated to provide alternately a positive and negative fluid pressure at an outlet port, the cylindrical valve member is rotated continuously in a single sense. While the fluid control valve disclosed in UK patent application No. 9522222.0 can be operated at high frequencies, the valve suffers from the disadvantage that it is difficult to ensure an adequate seal between the body and the valve member. This problem arises by virtue of requiring a cylindrical valve member which for a good seal requires a perfect axial alignment of the body and the valve member; perfect axial alignment only being achievable by accurate machining of the component parts which is time-consuming.
It is therefore an object of the present invention to at least partially mitigate the disadvantages of the prior art.
An embodiment of the invention provides a valve of simple construction which is capable of operation at high frequencies.
The present invention provides a valve for for controlling gas flow to ventilator or physiotherapy apparatus, comprising a body having first and second inlet ports and an outlet port characterised by a shutter plate rotatable with respect to said body and adapted selectively to interconnect said inlet ports to said outlet port, whereby said shutter plate is operable on rotation in a single sense to connect alternately said first inlet port to said outlet port and said second inlet port to said outlet port.
The use of a shutter plate allows sealing between the plate and the body to take place over a large area. It also reduces the need for time consuming highly-accurate machining. The relatively low moment of inertia of the plate, especially where it is made of thin light metal readily allows for rapid changes of speed.
Preferably, upon one full rotation of said shutter plate, said first inlet port is coupled to said outlet port, said second inlet port is coupled to said outlet port, said first inlet port is coupled again to said outlet port and said second inlet port is coupled again to said outlet port.
Advantageously, said body comprises a first body portion defining said inlet ports and a second body portion defining said outlet ports.
Preferably, said first body portion defines two chambers, each in communication with a respective one of said inlet ports, each chamber having a respective opening, and said shutter plate cooperates with said openings to effect connection of said outlet port and said inlet ports.
Advantageously, said first body portion has a face wall portion having said openings, said face wall portion having land portions between said openings.
Conveniently said shutter plate is generally circular, has a central axis of rotation, and defines at least two plate openings for cooperation with the openings of said body, whereby communication between said outlet port is established with said inlet ports.
Advantageously, the body has a circular flange upstanding around said face wall portion, the depth of the flange corresponding substantially to a thickness of said shutter plate, and the diameter of the flange corresponding to that of the shutter plate.
By this means, the sealing performance of the shutter plate is further improved.
Advantageously, said land portions are dimensioned and disposed so that in at least one position of said shutter plate, communication between said inlet ports and said outlet port is prevented.
Preferably the valve further comprises a shaft secured to said shutter plate.
Advantageously, said valve has an electric motor for driving said shaft.
Conveniently said motor is a stepper motor.
Alternatively said motor is a servomotor.
Conveniently control circuitry is provided for said motor.
Advantageously said control circuitry has means for varying the relationship between the time for which one inlet port is connected to the outlet port and the time for which the other inlet port is connected to the outlet port.
Conveniently, the control circuitry has means for varying the speed of rotation of the shutter plate.
According to a second aspect of the invention there is provided a ventilator or physiotherapy apparatus for use in the ventilation of the lungs of a patient, comprising an enclosure for receiving at least the chest region of the patient""s body, and a means for alternating the pressure in the enclosure to produce ventilation, said means comprising a positive fluid pressure source, a negative fluid pressure source and a valve comprising a body and a shutter plate, said body having first and second inlet ports and an outlet port, said shutter plate being rotatable with respect to said body and adapted selectively to interconnect said inlet ports to said outlet port, whereby said shutter plate is operable on rotation in a single sense to connect alternately said first inlet port to said outlet port and said second inlet port to said outlet port.
According to a third aspect of the invention there is provided a ventilator or physiotherapy apparatus for use in the ventilation of the lungs of a patient, comprising an enclosure for receiving at least the chest region of the patient""s body, a non-positive displacement source of positive and negative gas pressure and a valve connected to said pressure source, said valve comprising a body and a shutter plate, said body having first and second inlet ports and an outlet port, said shutter plate being rotatable with respect to said body and adapted selectively to interconnect said inlet ports to said outlet port, whereby said shutter plate is operable on rotation in a single sense to connect alternately said first inlet port to said outlet port and said second inlet port to said outlet port.
Advantageously, the pressure source comprises a blower.
Preferably, upon one full rotation of said shutter plate, said first inlet port is coupled to said outlet port, said second inlet port is coupled to said outlet port, said first inlet port is coupled again to said outlet port and said second inlet port is coupled again to said outlet port.
Advantageously, said shutter plate has a first position where said first inlet port is coupled to said outlet port, a second position where said second inlet port is connected to said outlet port and a third position intermediate said first and second positions where neither inlet port is coupled to said outlet port.
Preferably, in said third position of said shutter plate, said outlet port is substantially closed.
Conveniently, the valve further comprises a shaft secured to said shutter plate.
Advantageously, said valve has an electric motor for driving said shaft.
Conveniently said motor is a stepper motor.
Alternatively said motor may be a brushless dc motor.
Conveniently control circuitry is provided for said motor.
Advantageously said control circuitry has means for varying the relationship between the time for which one inlet port is connected to the outlet port and the time for which the other inlet port is connected to the outlet port.
Conveniently, the control circuitry has means for varying the speed of rotation of the shutter plate.
Conveniently said apparatus further comprises means for varying the pressure of said pressure source.
The present invention also relates to an oscillator for producing a pressure waveform, especially in ventilator or physiotherapy apparatus.
Ventilators fall into two classes, these being intermittent negative pressure ventilators (INPV) and intermittent positive pressure ventilators (IPPV). There are two principal kinds of negative pressure ventilator used in respiratory therapy, these being the body tank respirator (commonly called the iron lung) and the cuirass. There are many kinds of positive pressure ventilator such as volume and pressure-limited ventilators.
Positive pressure ventilators have many advantages over negative pressure ventilators. Notably, in requiring at most only tracheostomy or intubation of a patient, positive pressure ventilators provide good accessibility to the patient for patient care as compared to negative pressure ventilators which require total enclosure of at least the chest of a patient.
The intermittent positive pressure ventilation techniques do however have a number of significant disadvantages. For example, intubation of a patient requires highly skilled personnel both to insert and maintain the tube, and moreover causes secretion build up in the airways which requires the airways to be cleared regularly by suction. Both the introduction of a tube and the necessary suctioning frequently causes infection, which infection together with the secretion and the positive pressure applied to the lungs results in fibrotic changes in the lung tissue and a consequential reduction in lung compliance. The use of positive pressure also causes air leakage and barotrauma to the lung, and in creating a positive intrapulmonary pressure reduces the venous return and cardiac output. Indeed, the higher the pressure needed to ventilate a patient with a sick lung the greater the reduction there will be in cardiac output, which in turn will increase morbidity and mortality.
Techniques have been developed which reduce the tidal volume required to ventilate the lungs of a patient, and hence reduce the risk of barotrauma. One such technique is high-frequency ventilation (HFV). The mechanisms of high-frequency ventilation are not clearly understood, although it is well established that using this method carbon dioxide exchange can occur with tidal volumes less than a patient""s dead space. One particular high-frequency ventilation technique is high-frequency jet ventilation (HFJV) which is designed to deliver a high-pressure gas source through a small jet or cannula that is positioned in the main airway.
Such techniques however only partially alleviate the known problems. Recently, an oscillator has been devised which develops a pressure waveform capable of ventilating the lungs of a patient using a tidal volume of air so reduced as to lower the peak pressure of the cyclic pressure waveform required for ventilation and hence reduce the risk of barotrauma. This oscillator is disclosed in WO-95/32753. Whilst this oscillator does allow for the ventilation of the lungs of a patient with a reduced volume of air, it suffers from the problem that the action of the pressure waveform is not sufficient to clear satisfactorily the build-up of secretion from the airways.
It is thus a further aim of the present invention to provide an oscillator which is capable of ventilating the lungs of a patient with a reduced tidal volume and yet exhibit improved secretion clearance.
The present invention hence provides an oscillator for producing a pressure waveform, comprising a waveform generating means for producing a first, base cyclic pressure waveform having a second pressure waveform of positive pressure pulses of higher frequency superimposed thereon. The present invention hence provides an oscillator for producing a pressure waveform, comprising a waveform generating means for producing a first, base cyclic pressure waveform having a second pressure waveform of positive pressure pulses of higher frequency superimposed thereon.
Preferably, the waveform generating means comprises at least one apparatus in accordance with the third aspect of the invention.
Advantageously, the waveform generating means comprises a first apparatus in accordance with the third aspect of the invention for producing the first waveform, and a second such apparatus for producing the second pressure waveform.
Preferably, the waveform generating means comprises at least one apparatus in accordance with the third aspect of the invention.
Advantageously, the waveform generating means comprises a first apparatus in accordance with the third aspect of the invention for producing the first waveform, and a second such apparatus for producing the second pressure waveform.
With the present invention, improved secretion clearance is achieved by the superimposition of only positive pressure pulses on a base cyclic pressure waveform. It is the action of the positive pressure pulses which draws the secretion out of the airways. This contrasts with the oscillator disclosed in WO-95/32753 where a cyclic pressure waveform, i.e. a waveform comprising alternating positive and negative pressure pulses, is superimposed on another cyclic pressure waveform of lower frequency. While the action of the positive pressure pulses in that superimposed cyclic waveform is to draw secretion out of the airways this is counteracted by the action of the negative pressure pulses which is to draw the secretion back into the airways.